Tracheal Elongation in Birds-of-Paradise

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Abstract
The morphology of the elongated tracheae in 2 genera of paradisaeids is described. In Phonygammus the trachea is unelongated in young birds but as they age, males develop a long spiraled tracheal coil in the ventral body surface beneath the skin; females develop a shorter loop or coil and probably develop it more slowly. In Manucodia the trachea lengthens as a loop rather than a coil. It was found only in adult males and is probably species-specific, with minimum development in M. ater and maximum in M. comrii. The longest trachea recorded in Phonygammus is 828 mm; that in M. comrii is 627 mm (both minimum measurements). Speculations are offered on the physiological implications of this tracheal specialization. Both genera have approximately the same tracheal width (lumen diameter) as other passerines of similar body wt, and much smaller lumens than non-passerines with comparably elongated tracheae. The elongations may or may not be a serious physiological liability. Comments are made on the possible effects of tracheal elongation on these birds'' vocalizations.